Seeing as the number of possible outcomes from putting seven singledigit numbers together is 63, and 27 is around the middle, the odds for this are acctually fairly high. All in all, the chance for this is maybe around 5 times higher than the chance for trips.

Avg. of 0 through 9 is 4.5 This means the average roll will be somewhere between 4 and 5.
Multiply 4.5 by # digits you're rolling. This, on average, means that you'll roll a multiple of 4.5. These multiples are 4.5(1), 9(2), 13.5(3), 18(4), 22.5(5), 27(6), 31.5(7), 36(8), and 40.5(9)
As long as you roll even # of digits, odds in your favor that you'll be right.